The use of calcium oxide as a regenerable sorbent for CO2 capture has been a subject of
diverse research because of the enormous benefits it offers towards decarbonizing the
power industry particularly for post-combustion CO2 capture applications. These
benefits include: the low energy penalty imposed on power stations (estimated as 6- 8%), it’s benign nature in comparison with synthetic amine based sorbents, its CO2 removal ability to very low concentrations (<5%) at temperatures between 450-750°C, the availability of naturally occurring limestone which is extremely cheap and the application of deactivated sorbent as a source of cheap de-carbonised CaO to the cement industry.
However, calcium looping technology has its own shortfall which is mainly sorbent
deactivation with increasing loop cycle number, a consequence of mainly sorbent
sintering (as a result of employed high sorbent regeneration temperature >850°C) and to a lower extent sorbent fragmentation. This poses the need for fresh sorbent make-up and increases the cost of operation from cost of additional raw material and increased energy penalty from fresh sorbent calcination.
In order to successfully eliminate this downside of calcium looping, the behaviors of sorbents from different limestone precursors on sintering need to be understood. This
research aims to understand the role played by mineralogy and micro-structural
properties of precursor limestone on the sintering ability and attrition of the resultant
CaO sorbent post-cycling in order to inform material selection and to utilize naturally
occurring heterogeneities (e.g. silica and other impurities). This is to form a possible standard for screening limestone samples to ascertain their suitability for calcium
looping and thereby reduce the cost of the process through effective raw material
selection.
Chemical composition analysis was done using XRF and mineralogy analysis using
XRD. Textural properties were examined using MIP and nitrogen physisorption.
Sorbent’s CO2 conversion ability was observed using TGA and a bubbling fluidized
bed. Sintering was estimated in terms of decline in specific surface area and
qualitatively described using SEM and STEM. Sorbent attrition was estimated from the difference in sorbent mass within the 500-710 nm particle size range pre and post loop cycling.